Process for making a one-piece flexure for small magnetic heads

ABSTRACT

A process for making a gimbal formed integral with a load beam by through etching a H pattern at the end of the beam to define a pair of tabs connected by a pair of gimbal beams; half etching from the head direction one tab with an defined area masked to form a load button; and half etching the beam from the other direction to provide the proper gimbal stiffness. In practice, the head is glued to the other tab and load is applied through the button.

This is a divisional of application, Ser. No. 07/975,352, filed Nov. 12,1992, U.S. Pat. No. 5,331,489.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of rigid disc drive datastorage devices and more particularly to a process for making aone-piece flexure assembly for supporting the read/write heads of thedisc drive.

2. Brief Description of the Prior Art

Disc drives of the type known as "Winchester" disc drives are well knownin the industry. Such disc drive data storage devices typically containa stack of rigid discs coated with a magnetic medium on which digitalinformation is stored in a plurality of circular concentric tracks. Thestorage and retrieval of data--also called "writing" and "reading",respectively--is accomplished by an array of heads, usually one per discsurface, which are mounted on an actuator mechanism for movement fromtrack to track. The most common form of actuator used in the currentgeneration of disc drive products is the rotary voice coil actuator,which uses a voice coil motor (VCM) coupled via a pivot mechanism to theheads to access data on the disc surfaces. The structure which supportsthe heads for this movement is referred to as a head/gimbal assembly, orHGA.

The HGA in a typical disc drive consists of three components:

1. a slider, which features a self-acting hydrodynamic air bearing andan electromagnetic transducer for recording and retrieving informationon a spinning magnetic disc. Electric signals are sent to and receivedfrom the transducer via very small twisted copper wires;

2. a gimbal, which is attached to the slider and is compliant in theslider's pitch and roll axes for the slider to follow the topography ofthe disc, and is rigid in the yaw and in-plane axes for maintainingprecise slider positioning, and;

3. a load beam, which is attached to the gimbal and to a mounting armwhich attaches the entire assembly to the actuator. The load beam iscompliant in the vertical axis to, again, allow the slider to follow thetopography of the disc, and is rigid in the in-plane axes for preciseslider positioning. The load beam also supplies a downward force thatcounteracts the hydrodynamic lifting force developed by the slider's airbearing.

Since the introduction of the first Winchester disc drive, the physicalsize of the slider has been progressively reduced, first from theoriginal Winchester head to the so-called "mini-Winchester", and morerecently to the 70 and 50 Series heads, which are 70% and 50% the size,respectively, of the mini-Winchester slider. While these size reductionsare significant, the overall vertical dimension of the HGA has beendictated more by the slider-supporting mechanism than by the size of theslider itself.

The load beam and gimbal comprise an assembly generally known as a headsuspension, head flexure, or simply a flexure. An example of such aflexure is described in U.S. Pat. No. 4,167,765.

Historically, the gimbal and load beam are fabricated discretely. Thegimbal and load beam pieces are realized by chemically etching 300series stainless steel foil into the desired shape, and then the twopieces are attached by means of laser welding.

The general technology trend in disc drive data storage devices iscontinual shrinking of the physical size of the product while providingincreased data storage capacity. The down-sizing of the product hasrequired smaller components, especially the principal components such asdiscs, sliders and flexures. Additionally, disc drive designers seek toadd capacity to their designs by incorporating as many discs as possiblewithin defined package dimensions. As the number of discs in the unitincreases, the spacing between the discs decreases, thus further drivingthe need for smaller sliders and flexures.

Another industry trend is to provide the user of disc drives with highdata storage capacity at low cost. This requires developing improveddata recording technology and finding lower cost ways of manufacturingthe components of the disc drive.

The use of discrete gimbal and load beam components laser weldedtogether, as shown in the '765 patent, has become problematic in discdrives of the current 2.5", 1.8" and 1.3" generations of disc drives. Insuch units, the flexures must become thinner in order to allow desirableclose spacing of the discs, while the overlapping required to laser weldtwo discrete components necessitates increased thickness in the flexure.

Furthermore, the use of thinner gimbal and load beam componentsincreases the likelihood of residual stress caused by the laser weldingof the two components together. It has been found that laser weldingproduces residual tensile stress in the material local to the welds.This causes the flexure to distort. In the longitudinal direction, theflexure curls from the residual weld stress, and this makes it moredifficult to fit the flexure between closely spaced discs during themanufacturing process. Further, if the welds are not placedsymmetrically about the centerline of the flexure, the residual weldstress will cause a torsional distortion, or twisting, of the flexure.Such an flexure is undesirable since the twist will create a moment, ortorque, on the slider's air bearing, causing unwanted changes in theflying attitude of the head, and potentially rendering the assemblyunusable.

The welding process is also a substantial portion of the labor that goesinto the manufacture of a flexure, and it would, thus, be advantageousto eliminate the practice of making discrete gimbals and load beams andwelding the two together for cost reduction.

Since the gimbal and load beam components must overlap in flexures ofexisting art, the emphasis on reducing the thickness of the flexureassembly has most often focused on reducing the thickness of theindividual gimbal and load beam components. The thickest area of theload beam is the region known as the rigid beam, which usually featuresflanges along the outer edge along the longitudinal axis of the flexure.U.S. Pat. No. 4,996,616 teaches how a pair of drawn ribs can providereinforcement of the rigid beam section of the flexure. Unfortunately,the drawn pair of ribs of '616 requires that the flexure material bestrained to exceedingly high levels. Such stain can introduce cracks inthe drawn material, and high stresses in the material near the ribs.

Various attempts have been made to solve the problems inherent inwelding a gimbal and load beam together by devising a flexure in whichthe gimbal and load beam are formed from a single piece of material andwould thus require no welding. An example of such an integrated gimbaland load beam is presented in U.S. Pat. No. 4,245,267. A second exampleis known as the HTI Type 16, or T16, manufactured by HutchinsonTechnology, Incorporated. Both of these flexures have a gimbalincorporated into the load beam and, of course, no gimbal-to-load beamwelds. Both include a bonding surface on which adhesive is placed tosecure attachment of the slider to the flexure. A plurality of beams,etched into the load beam, connects this bonding surface to the loadbeam portion of the flexure and provides the desired gimbalcharacteristics.

One failing of the flexure of the '267 patent and the T16 flexurerelates to an element of flexure design commonly referred to as "loadpoint". Simply stated, load point refers to the single point of contactwhere the downward force of the load beam is applied to the slider.Proper selection of this load point ensures that the forces related tothe hydrodynamic air bearing of the slider are properly balanced. Inprior art flexures such as the one described in the '765 patent, loadpoint is developed by forming an upward-extending dimple in the gimbalbonding surface. The load beam contacts the spherical surface of thisdimple at a single point to allow proper gimbal action. In the case ofthe '267 and T16 flexures, however, a well defined load point is notprovided, and, thus, an undesirably wide range of variation in sliderflying characteristics is associated with these types of flexure.

A second fundamental problem with the '267 and T16 types of flexures isthat the downward force of the load beam is applied to the slider byplacing the gimbal beams into bending mode, and the gimbal beams musttherefore be stiff in bending mode. These same gimbal beams, however,must be compliant in bending mode to allow the proper gimballing action.This conflicting requirement results in designs that either work poorlyas a gimbal or become deformed under load.

A third problem with the '267 and T16 flexures is that the sliderbonding surface, in general, covers a large area over the center of theslider. The slider is attached to the flexure with an adhesive epoxy,and, in order to reduce the cure time of the adhesive, the assembly isusually heated in an oven. Since the slider and flexure are made ofdissimilar materials with different coefficients of linear thermalexpansion, thermally induced strains develop at the bond when theassembly cools. These strains can distort the slider and undesirablychange the flatness of the air bearing surface of the slider, thus, onceagain, introducing unacceptably wide variation into the flyingcharacteristics of the heads.

A need clearly exists for an improved slider-supporting flexure whichreduces the overall vertical height of the HGA, and which can bemanufactured in a simple, cost-effective manner.

SUMMARY OF THE INVENTION

The flexure produced by the process of the present invention is aone-piece load beam/gimbal assembly formed from a single piece ofmaterial. Features for providing the gimballing action, bonding of theslider to the flexure and location of the load point are all createdusing the processes of etching and half-etching. In the flexure producedby the process of the preferred embodiment, the gimbal end of theflexure is substantially rectangular, and a generally H-shaped openingis symmetrically located within the rectangular shape. The side railsformed between the H-shaped opening and the side edges of the gimbal arehalf-etched to reduce their thickness, and these side rails act as thegimballing mechanism of the flexure. A pair of tabs is formed in thegimbal end of the flexure on either side of the cross-member of theH-shaped opening, and one of these tabs is also half-etched to reduceits thickness. The full-thickness tab is used to bond the slider to theflexure, while the other tab serves to locate a load point contact whichis formed by not half-etching in the desired location for the loadpoint. The load beam portion of the flexure is stiffened by forming siderails or channels along the sides of the load beam portion of theflexure and by forming a tear-drop-shaped indentation in the load beam.Both the side rails and indentation are formed toward the side of theflexure on which the slider is mounted.

It is an object of the invention to provide a process for making alow-height flexure for mounting and supporting a slider.

It is another object of the invention to provide a process for making aflexure wherein the gimbal and load beam elements are formed from asingle piece of material, and require no welding.

It is another object of the invention to provide a process for making aflexure which is simple and inexpensive to manufacture.

It is another object of the invention to provide a process for making aflexure which incorporates a load point which is well defined and simpleto locate at an optimized location.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, benefits and objects of the invention can be bestunderstood from the following detailed description of the invention whenread in conjunction with the following drawings.

FIG. 1 is a plan view of a disc drive data storage device in which thepresent invention is particularly useful.

FIG. 2 is a plan view of the preferred embodiment of a flexure made inaccordance with the process of the present invention.

FIG. 3 is a detailed view of the gimbal portion of the flexure of FIG.2.

FIG. 4 is a sectional view of the gimbal portion of the flexure of FIG.2.

FIG. 4A is a sectional view of the gimbal portion of the flexure made inaccordance with the process of the present invention as assembled to aslider and in cooperative arrangement with a disc.

FIG. 5 is a partial sectional view showing the forming of the edge ofthe rigid beam portion of the flexure made in accordance with theprocess of the present invention.

FIG. 6 is a partial sectional view showing the forming of the rigid beamto increase stiffness.

FIG. 7 is a partial perspective view of the flexure made in accordancewith the process of the present invention as assembled to a sliderassembly.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and more specifically to FIG. 1, shown isa disc drive 2 in which the present invention is particularly useful.The disc drive 2 includes a base member 4 which, in cooperation with atop cover 6 (shown in partial cutaway), forms a sealed environment toprotect the delicate internal components from outside contaminants. Anumber of rigid discs 8 coated with a magnetic medium are mounted forrotation on a spindle motor (shown generally at 10). The surfaces of thediscs 8 hold a large number of concentric circular tracks to whichinformation is written and from which information is read. These tracksare represented by the innermost and outermost tracks, designated bybroken lines 12 and 14 respectively.

An actuator body 16 is adapted for rotation about a pivot shaft 18 by avoice coil motor (VCM), shown generally at 20. On the side of theactuator body 16 opposite the VCM 20 are a number of head mounting arms22 to which are attached a plurality of flexures 24 for the mounting ofsliders 26. Power for the VCM 20, as well as the signals used to readand write data, is passed via a printed circuit cable (PCC) 28.

Turning now to FIG. 2, shown is a plan view of a flexure 30 made inaccordance with the present invention. The flexure 30 is symmetricalabout a longitudinal axis 31 and is made up of four distinct majorareas:

1. a gimbal/slider mounting area 32;

2. a rigid beam 34;

3. a pair of compliant beams 36, and;

4. an attachment surface 38.

The entire flexure 30 is formed from a single piece of 300 series fullhard stainless steel, preferably 0.0025 inches in thickness, andmanufactured using well known chemical etching processes.

A pair of alignment holes 40, 42 aid in fixturing the flexure during theprocess of bonding the slider (not shown).

The attachment surface 38 in the example of FIG. 2 is shaped to beattached to a particular type of mounting plate to provide a strongsurface for attachment of the entire flexure head assembly to the headmounting arms 22 of the actuator body 16. While the specific method ofmounting the flexure is not considered a part of this invention, itshould be noted that this attachment surface 38 could easily be adaptedfor use with other types and designs of mounting apparatus.

The direction of movement of the disc relative to the flexure is shownby arrow A. Any slider attached to the flexure of the present inventionis therefore assumed to have its leading edge closest to the attachmentsurface 38 and its trailing edge closest to the free end of thegimbal/slider mounting area 32.

The gimbal/slider mounting area 32, the rigid beam 34 and the pair ofcompliant beams 36 will each be discussed in turn below.

FIG. 3 shows a detailed view of the gimbal/slider mounting area 32 ofthe flexure of the present invention with a slider 48 attached. As waspreviously mentioned, the flexure of the present invention is formed bythe process of chemical etching. In usual chemical etching processes,the material to be etched is first coated on both sides with a materialcalled resist. The resist is patterned using a stencil and exposing theresist to a light source. Unexposed resist is then stripped away,leaving exposed metal that will be etched away in the presence of anacid-like etchant. Both sides of the material are treated in thismanner, with the pattern on both sides being very accurately aligned.This is the process used to define the perimeter outline of the flexureof the present invention and all through openings.

In half-etching, the pattern of the stencil on one side of the materialis dissimilar to that on the other side. This also is a well knowntechnique for etching text, art or half-tone photographs into sheetmetal. It is known that if the area to be half-etched is large--that is,it has a length or diameter many times that of the materialthickness--the depth of the half-etching will be approximately sixtypercent that of the material thickness.

The process of full- and half-etching is used to produce several of thefeatures of the flexure of the present invention. For instance, as canbe seen in FIG. 3, an H-shaped opening 44 has been etched completelythrough the material, and areas beside the vertical legs and on one sideof the cross member of the H-shaped opening 44 have been half-etched.Specifically, the area shaded lower-left-to-upper-right is half etchedon the near side of the material, while the area shadedlower-right-to-upper-left has been half-etched on the far side of thematerial. Since the overall thickness of the material is approximately0.0025 inches, these half-etched areas are reduced in thickness to about0.0010 inches thick.

This half-etching process forms a pair of gimbal beams 58 which will bediscussed in detail below.

The etching process also forms a slider mounting tab 46 to which theslider 48 is adhesively bonded. As can be seen in the figure, thisbonding is thus done only in that area of the slider 48 closest to thetrailing edge of the slider 48. In prior art flexures, such as theflexure of the '765 patent, the bonding surface was generally centeredon the slider and occupied a large percentage of the entire top surfaceof the slider. The location of the bonding surface in the flexure of thepresent invention has several advantages:

1. In prior art flexures, the air bearing surface distortion created bythermal strain during oven curing of the adhesive was significantlylarge, since the bonding was done in the center of the slider and over arelatively large area of the slider. In general, the smaller the bondingsurface and the farther the bonding surface is removed from the centerof the slider, the lower the amount of air bearing distortion caused byoven curing of the adhesive. With the flexure of the present invention,the bonding surface is located as far as possible from the center of theslider--in fact, with a 50% slider, the bonding surface includes onlythat area within approximately 0.025 inches of the trailing edge of theslider--thereby providing minimal air bearing surface distortion.

2. The flexure of the present invention provides great ease ofinspection of the adhesive bond between the slider and the flexure. Inprior art flexures, the bonding surface is located between the sliderand a separate load beam. The load beam obstructs the view of thebonding surface, which makes it difficult, if not impossible, to confirmthe presence of adhesive fillets around the entire perimeter of thebonding surface. In the flexure of the present invention, no such visualobstruction exists.

3. The structure of the flexure of the present invention facilitatesconductive heating of the bonding surface to speed the curing of theadhesive. In prior art flexures, the adhesive that secures the slider tothe flexure was typically heated in a convective oven to hasten adhesivecuring. Conductive heating, also known as "hot foot bonding" cansubstantially reduce the curing time, but was generally not practical inprior art flexures since the load beam prevented direct access to thebonding surface. In the flexure of the present invention, the bondingsurface is completely accessible for conductive heating, thuspotentially reducing the time required to cure the adhesive securing theslider to the flexure.

4. The flexure of the present invention also provides for greater bondstrength than could be realized in prior art flexures. For a variety ofreasons, the bonding surface of prior art flexures could not extend overthe full width of the slider. Since, in general, the wider the bond, thegreater the bond strength, and since the inventive flexure allows thebond to extend across virtually the entire slider, the flexure of thepresent invention can be expected to provide the maximum bond strengthfor a given size of slider.

The H-shaped opening 44 also forms a load point tab 50 on the oppositeside of the cross-member of the opening from the slider mounting tab 46.The load point tab 50 transmits the load force of the flexure to theslider 48 via a load point button 52, or load supporting protrusion,which is formed by masking the desired location and size prior tohalf-etching, so that the load point button 52 maintains the fullthickness of the flexure material. Since the load point tab 50 ishalf-etched on the far side of the material as viewed, this has theeffect of creating a "pin" which projects toward and contacts the top ofthe slider 48. The load point button 52 should be as small in area as ispossible given the manufacturer's capability in chemical etching. Thisdimension has been found currently to be about 0.002 inches, whichcauses the load force of the flexure to be applied to the slider at asclose as possible to a single point. The location of this single pointis selected to provide the desired flying characteristics for theparticular design.

Several significant advantages are realized by the flexure of thepresent invention over flexures of the prior art:

1. The load point button 52 of the flexure of the present invention canbe more exactly located relative to the slider than can the load pointsof prior art flexures. In prior art flexures, the load point istypically a spherical formed projection, or dimple, in the approximatecenter of the slider bonding area which contacts the load beam at asingle point at the apex of the projection. However, the exact apex ofthe spherical projection, and therefore the exact load point, isdifficult to determine. The exact location of the half-etched load pointbutton 52 of the flexure of the present invention is, by comparison,easy to determine.

2. With the load point button 52 of the flexure of the present inventionthere is less variability in protrusion height. In formed protrusions ofthe prior art, the tolerance on the protrusion height has typically been±0.0010 inches. In the flexure of the present invention, thisvariability has been reduced to the order of ±0.0002 inches.

3. There is less variation in the location of the load point with theflexure of the present invention than in prior art flexures. In priorart flexures, the spherical protrusion is generally formed as asecondary step in the manufacturing process after the shape and size ofthe flexure have been determined by etching. This means that thelocation where the forming occurs varies with respect to the datum edgesof the flexure, since some clearance must be provided between the datumedges of the flexure and the location surfaces of the forming die. Inthe flexure of the present invention, the edge datums and load pointbutton coexist on the same artwork pattern, or mask, thus substantiallyreducing the variability in the location of this feature.

4. The flexure of the present invention provides greater flexibility tomodify the desired location of the load point than do prior artflexures. The location of the load point relative to the slider iscritical to obtain the desired flying attitude of the slider.Occasionally during the development of a new disc drive product, or themodification of an existing product, it may become necessary to changethe location of the load point. It has been economically impractical tomodify the location of the formed spherical projection of prior artflexures due to the required retooling and new fixtures. Therefore,modifications in load point location in prior art flexures havegenerally been accomplished by modifying the bonding fixtures used toalign the slider and flexure during the adhesive bonding procedure. Withthe flexure of the present invention, it is possible to change thelocation of the load point button 52 by simply changing the artworkpattern, or mask, used in the etching process. Generally speaking,master artwork patterns are far less expensive to modify than fixturesand hard tooling.

The actual shape of the load point button 52 can be easily determined bythe artwork pattern, and can thus be round, oval or oblong should suchbe desired. In some cases it may be desirable or necessary to radius theedges of the load point button 52. This can be done by spanking thebutton with a suitably shaped die. An alternative method would beetching a half-tone transition between the top of the button and thefull depth of the half-etching. The half-tone pattern could consist ofsmall circles whose size and spacing are related to their distance fromthe center of the button, or rings whose line width and line spacing arealso related to their distances from the button center.

The exact location of the load point button 52 is determined to providethe desired flying attitude of the slider. Typically, this location is afew thousandths of an inch away from the center of the slider toward thetrailing edge. The desired load point is also frequently offset from thelongitudinal centerline of the slider to compensate for velocity vectorfield variations and such known factors as the torsional bias applied bythe tiny wires used to carry read/write signals to and from the head. Ifsuch an offset in load point location is incorporated in the artworkpattern, it can be extremely difficult to determine the direction ofthis offset visually. Such a determination is necessary because flexuresintended for use on opposite sides of the discs would typically havethis offset in opposite directions. Therefore, the artwork pattern caninclude an offset determination hole 54 which would be located at anobviously assymmetrical location and would indicate toward which side ofthe flexure the load point button 52 was offset.

Another feature of the flexure of the present invention is a slideralignment inspection hole 56. This slider alignment inspection hole 56may be round or elongated as shown in the figure. Such a feature isdesirable when measuring the alignment of the slider to the flexure witha vision based metrology system. Such measuring systems depend on highcontrast at edge locations, and a through hole will allow a portion ofthe slider edge to be silhouetted by a profile light source when theslider is properly aligned with the flexure.

FIG. 3 also shows a pair of gimbal beams 58 formed adjacent the verticallegs of the H-shaped opening 44. It should be recalled that these gimbalbeams 58 were half-etched on the near side of the material as viewed inFIG. 3 to a thickness of approximately 0.0010 inches. Since the slider48 is bonded to the slider mounting tab 46, and load force is applied tothe slider 48 through the load point button 52 on the load point tab 50,it will be apparent to one skilled in the art that the gimbal beams 58will allow the necessary gimballing action of the flexure while stillmaintaining needed stiffness in the desired axes. To ensure properoperation of the gimbal beams 58, it is desirable to have the plane ofthe gimbal beams 58 coincident with the point of contact of the loadpoint button 52 with the slider 48. This is best achieved in the flexureof the present invention when the half-etching of the gimbal beams 58and the load point tab 50 are on opposite sides of the material. In someinstances, it may be desirable to introduce some forming of the loadpoint tab 50, since this tab is subject to some deflecting when underload. The amount of deflection of the load point tab 50 can be foundusing the following formula: ##EQU1## where: F is the load force

L is the distance from the load point button to the root of the loadpoint tab;

E is the modulus of elasticity of the flexure material;

W is the width of the load point tab at its root,and;

T is the thickness of the load point tab.

The slope at the end of the load point tab can be found using theformula: ##EQU2##

Using algebra, it is possible to show that the end of a deflected beamcan be made tangent to the root of the beam if the beam is formed at apoint one-third the length of the beam from the base of the beam.

The preferable method of forming the single bend in the load point tab50 is by stamping. In volume manufacturing, it may be necessary, due tovariation in material thickness and half-etch depths, to overbend andthen relax back to the desired angle using, for instance, infraredheating.

An example of the calculations to determine the design of the load pointtab follows.

Assume:

Load point is offset 0.005" from center of slider toward the trailingedge.

Half length of the slider is 0.040".

Clearance (end of slider to end of tab) is 0.005".

Tab base width is 0.058.

Tab length (L)(base to load point) is 0.005"+0.040"+0.005"=0.050"

Load force (F) is 3 grams.

Deflection under load at the load point can be found using the followingformula: ##EQU3## where I is the bending moment of inertia.

Solving the equation with the above assumptions:

Slope under load at the load point can be found using the ##EQU4##following formula: ##EQU5##

Solving equation (4) with the above assumptions: ##EQU6##

Therefore, if the load point tab 50 is preformed with a 3.546° bend at apoint one-third of the distance from the base of the tab to the loadpoint button 52, it can be assumed that the actual contact point betweenthe load point button 52 and the slider 48 will lie substantially in theplane of the gimbal beams when the assembly is under designed loadconditions.

Referring now to FIG. 4, the desired forming of the load point tab 50 isillustrated by a detail sectional view taken along line 4--4 of FIG. 3.As can be seen, the load point tab 50 is bent in the direction of theslider (not shown) at an angle of approximately 3.546°. Because of thisbending, when the slider is mounted on the slider mounting tab 46, andthe entire assembly is brought into its intended relationship with thespinning disc of the disc drive, the bottom of the load point button52--and thus the top surface of the slider--will lie substantially inthe plane occupied by the gimbal beams 58. This relationship is bestseen in FIG. 4A, wherein a slider 48 has been bonded to the slidermounting tab 46 and the entire assembly brought into operationalrelationship to a disc 8.

Similarly, various characteristics of gimbal beam stiffness can also becalculated.

Assume:

L (length of the gimbal beams)=0.106".

r (distance from the load point button contact to the gimbal beamtrailing edge)=0.053".

w (width of one gimbal beam)=0.010".

t (thickness of the gimbal beam)=0.001".

The stiffness of the gimbal can be calculated in various axes using thefollowing formulae: ##EQU7##

An analysis of these stiffness figures reveals that the gimbal isrelatively compliant in the pitch and roll axes, as is desireable forfollowing minor variations in the surface of the disc, while it is verystiff in the yaw axis, since any compliance in yaw would result inmisalignment of the head from the desired on track position. Similarly,the across-track stiffness and along track stiffness are very high tomaintain on-track stability.

It should be noted that the stiction stress calculation is normalized toone gram of stiction force, and since the yield stress limits of thematerials envisioned is on the order of 200,000 psi, only an amount ofstiction which would be totally fatal to the entire disc drive couldcause the gimbal to fracture.

It should also be noted that in the flexure of the present invention,the only gimbal forming required is a single bend in the load point tab50. Prior art flexures universally require forming a load pointprotrusion, sometimes referred to as a "dimple" in the gimbal bondingsurface, which invariably effected the flatness of the gimbal bondingsurface. In addition, prior art flexures have some type of offsetforming to allow the gimbal bonding surface to be out-of-plane from therest of the flexure by an amount equal to the dimple height. Thisout-of-plane forming introduces stresses and distortions into the gimbalstructure, and in some instances, cracking of the gimbal can occur. Suchproblems are totally absent in the flexure of the present invention.

An additional benefit of the gimbal of the flexure of the presentinvention is a substantial reduction in the distance between the centerof gravity of the slider body and the point of contact of the load pointprotrusion. When rapid accelerations occur in the head positioningactuator of the disc drive, some undesirable changes in flying attitudeoccur. The inertia of components such as the slider can create externalmoments on the air bearing during such events. A general rule-of-thumbis that the magnitude of these moments is directly proportional to thedistance between the center of gravity of the slider and the point ofcontact of the load point protrusion. In prior art flexures, it has notbeen possible to have the load point contact the slider and still havethe contact point coplanar with the gimbal beams, as it should be forminimal gimbal stiffness in the desired axes. Prior art flexures used adimple formed on the opposite side of the bonding surface from theslider to provide a contact point for the load beam, which meant thatthe load point was displaced from the slider by at least the height ofthe dimple. In the flexure of the present invention, the load pointbutton 52 directly contacts the slider 48.

Referring now back to FIG. 2, the rigid beam 34 portion of the flexureof the present invention is symmetrical about the longitudinal axis 31of the flexure and generally trapezopidal in shape with the small baseof the trapezoid adjacent the gimbal/slider mounting area 32. Thegeneral function of the rigid beam 34 is to transfer the downward forcegenerated by the pair of compliant beams 36 to the gimbal/slidermounting area 32. As such, it is important that the rigid beam 34 beextremely stiff to resist both bending along the longitudinal axis 31and twisting about the longitudinal axis 31.

In order to impart high stiffness to the rigid beam 34, the material ofthe rigid beam 34 is formed to substantially increase the sectionalmoment of inertia. Along the tapered edges of the rigid beam 34 areV-shaped channels 60, with the apex of the V extending in the directionof the slider. FIG. 5 is a partial sectional view of one of thesechannels 60 taken along the general line 5--5 in FIG. 2. The channels 60are typically formed 0.0045 inches out-of-plane. The distal edge of theV channel may be approximately level with the plane of the unformedmaterial as shown at 62. In some cases it may be advantageous to havethe distal edge of the V channel extend beyond the plane of the unformedmaterial, since the bending moment increases in the direction away fromthe gimbal, and therefore a higher sectional moment of inertia isdesirable. In such a case, the distal end of the channel could be formedat the point shown by the designator 64. In either case, the preciselocation of the distal end of the channel 60 is determined by theartwork mask used to etch the outer edge of the flexure.

A further, albeit slight, increase in sectional moment of inertia can berealized if the distal edge of the V channel 60 is not etched at a rightangle to the material surface, as is typical in prior art flexures. Byusing two differing artwork patterns during etching, it is possible toetch a "beveled" edge. Ideally, the angle of this bevel should be suchthat the etched edge, after forming, will be substantially parallel tothe plane of the unformed material. This approach is shown in FIG. 5 atthe distal edge of the channel 60. In the figure it can be seen that thevery edge of the material of the flexure is half-etched to form a "step"which, after the forming of the channel 60, lies substantially parallelto the surface 66 of the unformed material. This stepped edge providesthe maximum "edge length", and thus contributes to the stiffness of therigid beam 34.

While the preferred cross-sectional shape of the channel is a V, itshould be readily apparent that other shapes could be employed toachieve a high sectional moment of inertia.

Additional stiffening of the reinforced beam can be obtained by drawingthe center section of the rigid beam 34 out-of-plane. In the plan viewof FIG. 2, this stiffening area 68 is somewhat teardrop shaped, andoriented in the same direction as the tapering of the rigid beam 34, butother shapes for the stiffening area can be readily conceived. Thestiffening area 68 is drawn out-of-plane approximately the same amountas are the channels 60.

The rigidity of the rigid beam 34 is optimized when the area of thedrawn material in the stiffening area 68 is substantially equal to thearea of the unformed material. As shown in FIG. 6 which is again apartial sectional view along line 5--5 of FIG. 2, between the drawn andundrawn material is a transition region 70 which is strained when thematerial is formed. In order to prevent cracking in the transitionregion 70, it has been found that the strain level should be kept to amaximum of 5 percent of material tensile strength. The minimum length,x, for a transition region 70 which meets this requirement can be foundby using the following formula: ##EQU8## where: x is the length of thetransitional region, and

d is the distance out-of-plane that the material is drawn.

The channels 60 on the edges of the rigid beam 34 also serve as arouting path for the wires (not shown) which carry the read/writesignals to and from the head mounted in the slider. As can be seen inFIG. 2, the ends 72 of the channels 60 nearest the gimbal/slidermounting area 32 are formed at an acute angle to the line 74 whereforming of the channels 60 begins. This angle is to facilitate therouting of the head wires into the channels 60.

FIG. 7 is a detail perspective view of the gimbal end of the flexure ofthe present invention with a slider attached. As can be seen, the wires76 that carry the read/write signals to and from the transducer (notshown) are attached to the slider 48 on its trailing surface 78 and arerouted in a loop to the channel 60 along the side of the flexure. Sincethe flexure is symmetrical about its longitudinal axis, this allowsupward-facing and downward-facing flexures to carry the wires 76 on thesame side relative to the actuator, thus easing connection to the pcc(28 in FIG. 1) which carries these signals to and from the disc.

Referring again to FIG. 2, attached to the large base of the trapezoidshaped rigid beam 34 are a pair of compliant beams 36. One function ofthese beams 36 is to serve as a low friction pivot, or hinge. Anotherfunction is to provide the downforce that counteracts the hydrodynamiclift of the air bearing surfaces of the slider. In the preferredembodiment, the two compliant beams 36 are each 0.100 inches long and0.040 inches wide. The distance between the outer edges of the twocompliant beams 36 is 0.200 inches at the root of the beams, with thisdistance decreasing in the direction of the gimbal/slider mounting area32 at a rate substantially equal to the tapering of the rigid beam 34.The distance from the root of the two compliant beams 36 to the loadpoint button (52 in FIG. 3) is 0.610 inches.

The two compliant beams 36 are formed after the flexure is etched suchthat the slider will be encouraged toward the disc when the entirehead/gimbal assembly is installed in the disc drive. The preferredmethod of forming the two compliant beams 36 is described in detail inU.S. Pat. No. 5,065,268, issued Nov. 12, 1991, assigned to the assigneeof the present invention and incorporated herein by reference.

A comparison between a typical prior art flexure/slider assembly and aflexure/slider assembly made in accordance with the present inventionshows clearly that the inventive flexure can contribute significantly tothe reduction of separation between the flexure/slider mounting surfaceand the disc surface, thus allowing closer disc spacing which can leadto either lower overall drive height or additional discs within a givenpackage dimension. In prior art flexure/slider assemblies, the minimumflexure mounting surface to disc surface dimension is the arithmetic sumof the following thicknesses:

    ______________________________________                                        Slider thickness:                                                                             0.017   ± 0.001                                            Gimbal dimple height:                                                                         0.0055  ± 0.0005                                           Load beam thickness:                                                                          0.0025  ± 0.00025                                          Total:          0.0250  ± 0.00175 worst case,                                                      ± 0.001146 three sigma.                            ______________________________________                                    

Using the flexure of the present invention, the same minimum dimensionis the sum of the following thicknesses:

    ______________________________________                                        Slider thickness:                                                                             0.017   ± 0.001                                            Flexure thickness:                                                                            0.0025  ± 0.00025                                          Total:          0.0195  ± 0.00125 worst case,                                                      ± 0.001031 three sigma.                            ______________________________________                                    

From these figures, it is apparent that, not only does the flexure ofthe present invention allow approximately a 22% reduction in thisdimension, but that worst case tolerance error has also beensignificantly reduced.

It is also apparent that the flexure of the present invention is lessexpensive to manufacture since the need for gimbal-to-load beam weldinghas been eliminated. Laser welders are expensive pieces of capitalequipment in their own right, with low throughput, and require expensiveand precise fixturing to align the separate pieces for the weldingprocess. Moreover, as previously stated, the welds produced by laserwelding contain high residual stresses that can distor the flexure,reducing quality levels.

In summary, the inventive flexure can contribute to a reduction indisc-to-disc spacing--with either reduced drive height or increaseddrive capacity--while lowering costs and improving the precision of thedisc drive.

While a specific embodiment of the present invention has been discussed,numerous variations--for instance in materials, proportion of elements,and methods of manufacture--are possible. For example, the flexure ofthe present invention could be realized from beryllium copper ortitanium, the flexure could be made proportionally wider to improvein-plane bending resonant frequency, or the flexure could bemanufactured by stamping with reactive etching to reduce the thicknessof material in desired areas.

It will be clear that the present invention is well adapted to carry outthe objects and attain the ends and advantages mentioned as well asthose inherent therein. While a presently preferred embodiment has beendescribed for purposes of this disclosure, numerous changes may be madewhich will readily suggest themselves to those skilled in the art andwhich are encompassed in the spirit of the invention disclosed and asdefined in the appended claims.

What is claimed is:
 1. A method of making a disc drive magnetic headmounting flexure from generally planar materialcomprising:through-etching an H-pattern at the end of a load beam todefine a load point tab, a slider mounting tab and connecting gimbalbeams; half-etching the load point tab from a first material side afterfirst having masked a load point button area on the load point tab sothat a load point button remains unetched; and half-etching saidconnecting gimbal beams from a second material side, opposite said firstmaterial side.
 2. The method of making the disc drive magnetic headmounting flexure of claim 1 further including:forming a bend in the loadpoint tab towards said first material side.
 3. The method of making thedisc drive magnetic head mounting flexure of claim 1 furthercomprising:forming a radius on the load point button formed on said loadpoint tab.
 4. The method of making the disc drive magnetic head mountingflexure of claim 1 further including:through-etching a slider alignmentinspection hole in said load point tab.